Jason Tarver on the sidelines in Stanford's game against San Jose State at Stanford Stadium, September 3, 2011
STANFORD, CA - SEPTEMBER 3: Stanford defeats San Jose State 57-3 at Stanford Stadium, September 3, 2011 in Stanford, California.

In 2001 Jason Tarver had finished three years as a graduate assistant on UCLA coach Bob Toledo's staff. He had a master's degree in biochemistry and molecular biology.

He could have gone into drug design or research, or to medical school. He had thought about being an orthopedic surgeon after shattering his knee as a high school safety.

But there he was, sitting at a conference table at the 49ers' headquarters. Bill Walsh was there. So was Steve Mariucci, then the head coach, along with others.

"Why the heck do you want to be doing this?" they asked.

He's been asked the question quite a few times over the years in a career that led him this year to become co-defensive coordinator at Stanford. He and Derek Mason guide a unit that leads the nation in run defense.

Tarver had gotten his interview with the 49ers through the coaching network. After a long talk, they offered him the keys to a club van and told him he could either take them, go to his father's home in Livermore and come back to work - or take a job he had been offered with the Green Bay Packers. He said, "Give me the keys."

Here's all you need to know about his skills as a coach: He was hired by Mariucci, then retained by Dennis Erickson, Mike Nolan and Mike Singletary. Counting Jim Tomsula, who coached the 2010 finale after Singletary was fired, he worked for five head coaches in one organization.

He says he caught the coaching bug at West Valley College in Saratoga. He had gotten a scholarship to play at Santa Clara, which dropped football a few months later. He took a detour to play at the junior college and later coached there while completing his degree.

"I really love the look on guys' faces when you help them make a play," he said. "It's almost better than doing it yourself. That's what really made me want to do this.

"And then, I like to see 22 guys running around and see how it all fits together. That's a puzzle that's always fun. It's a moving puzzle every single play, and you've got to figure it out between the plays."

There's even a parallel between football and molecular biology, he said. "The process - making the complex seem simple so that you can execute it. In research, you apply the rules you know to reactions and try something new. It's the same thing when you teach a guy how to run a blitz. He may deal with something new, but as long as he starts the process correctly, then you deal with what happens."

Tarver is the son of a research scientist at Lawrence Livermore National Laboratory and an elementary school teacher. Jason's light reading while growing up was sometimes his father's papers on explosives.

His father used to work at Stanford, and Jason's earliest football memories are of watching John Elway at Stanford Stadium.

He and his wife, Katie, a former gymnastics coach, have two sons, Merrick, 4, and Keegan, 1. "She's a much better athlete than I am," Tarver said. "I hope the boys get their ability from her."

Briefly: The kickoff for Stanford's Oct. 8 home game against Colorado has been scheduled for 4:30 p.m.